20110924-直接高斯消元法

 

 1 #include  < stdio.h >
 2 #include  < math.h >
 3 #include  < stdlib.h >
 4 /**/ /*
 50.500000 1.100000 3.100000
 60.000000 -10.040000 -24.500000
 70.000000 0.000000 -12.284024
 8-2.600000
 91.000000
102.000000
11请按任意键继续. . .
12*/
13 #define  n 3
14 double  a[ 3 ][ 3 ] = {{0.5,1.1,3.1},{5,0.96,6.5},{2,4.5,0.36}} ;
15 double  b[ 3 ] = {6,0.96,0.02} ;
16 double  m[ 3 ][ 3 ];
17 double  x[ 3 ] = {0,0,0} ;
18 int  k,p;
19
20 int  main() {
21    for(k=0;k<n-1;k++){
22            if(a[k][k]==0)  break;
23            else{
24                     for(int i=k+1;i<n;i++){
25                             m[i][k]=a[i][k]/a[k][k];
26                             for(int j=k;j<n;j++){        
27                             a[i][j]=a[i][j]-m[i][k]*a[k][j];
28                             }
29                             b[i]=b[i]-b[k]*m[i][k];
30                     } 
31            }        
32    }
33    for(int i=0;i<n;i++){
34            for(int j=0;j<3;j++){
35            printf("%f ",a[i][j]);}
36            printf("\n");        
37    }
38    //huidai--有错 
39    x[n-1]=b[n-1];//Right.. 
40    for(int i=n-1;i>=0;i--){//where is the error
41          double sum=0;//ok.Vectory.
42          for(int j=i+1;j<n;j++){//Be careful while using for loop!!!
43                sum+=a[i][j]*x[j];
44          }
45          x[i]=(b[i]-sum)/a[i][i];
46    }
47    
48    for(int i=0;i<n;i++){
49            printf("%3.2f\n",x[i]);        
50    }
51    
52    system("pause");
53}
54